Process of producing finely divided metals and alloys



United States Patent 3,369,886 PROCESS OF PRODUCING FINELY DIVIDED METALS AND ALLOYS Gershon Metzger and Hugh H. Horowitz, Elizabeth, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Sept. 23, 1964, Ser. No. 398,786 9 Claims. (Cl. 75-.5)

This invention is directed to a process of producing finely divided metals. In particular, this invention is directed to a process wherein metal salts are reduced in solution to provide finely divided particles which do not agglomerate. More particularly, this invention relates to a process wherein finely divided metals are precipitated from a solution of their salts in conjunction with the precipitate of aluminum hydroxide and the finely divided metals produced by this process.

One of the problems facing the art has been the production of finely divided metals for use in various catalytic processes. Numerous methods for producing metals with large surface areas and activating such finely divided metals are known to the art such as reducing the metals from a solution of a metal salt with an alkali metal dissolved in an organic solvent, the reduction of metals from an aqueous solution with an alkali metal borohydride, and the high temperature reduction of metals with hydrogen and/or carbon monoxide. Such prior art procedures have provided finely divided metals. However, the surface areas of such precipitates are limited by the growth of metal crystallites during the precipitation which limits catalyst activity.

It has now been found that finely divided metals having a very large surface area can be prepared with minimal particles agglomeration relative to the prior art methods. According to the instant invention, salts of the desired finely divided metals are dissolved in a suitable solvent. An aluminum compound is then added to the solution. After the addition of the aluminum compound, such as an aluminate salt, a reducing agent is added under conditions so that the reduction of the metals and precipitation of aluminum hydroxide occur simultaneously. The resulting precipitate is treated with a basic solution and then dried. The resulting finely divided metal has a very large surface area.

The reducing agents to be used in this invention are nonmetallic in nature and do not liberate hydrogen or hydrogen-containing compounds from water, but do react to form an acid as the metal salt is reduced. As examples of reducing agents which can be used in the practice of this invention, the following can be named: formaldehyde, hydrazine, hydroxylamine, methanol, hydrogen, propanol, acetaldehyde, hydroquinone, diborane and isopropanol. Reducing agents which liberate hydrogen or hydrogencontaining compounds upon reaction such as sodium, sodium borohydride or methyl magnesium halide could be used provided one started with a cationic aluminum salt.

The process of this invention can be used to prepare finely divided particles from solutions of the salts of the metals of Groups IV-B, V-B, VI-B, VIIB, VIII, IB, II-B, III-B, IV-A and V-A, as shown in the Periodic Chart of the Elements, pages 394 and 395, of the 38th edition of the Handbook of Chemistry and Physics. The metal salts of the aforesaid groups may be reduced singularly or in combination, thereby providing a precipitate comprising more than one element. The resulting precipitate may be either the metal in the zero valence state or compounds of the metal in a valence state lower than the metal in the salt.

The aluminum compound which is to be added to the salt solution can be an alkali metal aluminate, such as sodium, potassium or lithium aluminate. In addition to the aluminates, there can be added to the salt solution an aluminum-containing compound such as aluminum halide or aluminum nitrate in addition to a strong base thereby providing aluminum hydroxide which can be titrated with a strong alkali such as KOH, NaOH or LiOH in order to dissolve a portion of the Al(OH) in the solution. At this point, the reducing agent can be added and the process will continue as hereinafter described. The aluminum-containing compounds which can be added to the solution include alkali metal aluminates, aluminum halides and aluminum nitrate which can be dissolved in sodium or potassium hydroxide to form sodium or potassium aluminate. Aluminum metal and an alkali metal hydroxide can also be added to the salt solution of the metal to be precipitated and then the reducing agent can be added.

The process of the instant invention is carried out by putting a salt or salts of the desired finely divided metals into solution, adding an aluminum-containing compound such as an alkali metal aluminate and then adding a nonmetallic reducing agent thereby simultaneously precipitating the metal and aluminum hydroxide.

The resulting precipitate is then treated with an acid or base to remove the aluminum hydroxide from the precipitate. It is, of course, obvious that the aluminum hydroxide will be dissolved with a solution that does not attack or dissolve the metal. The metal is then washed and dried. The metal can be used for the desired purpose,

usually as a catalyst in a chemical reaction. In a preferred method of conducting the process of the instant invention, after the addition of the aluminate salt to the solution, the solution should be titrated with acid until aluminum hydroxide has begun to precipitate so thatthe acid formed during the reduction step will immediately cause further precipitation of the aluminum hydroxide. The metal-aluminum hydroxide precipitate of this invention can be dried without treating with a basic solution, calcined and formed into electrodes for use in batteries, electrochemical reactions or in fuel cells.

The finely divided metals produced in accordance With the instant invention can be used as catalysts in chemical reactions such as polymerization, hydrogenation, dehydrogenation, electrochemical oxidation or reduction reactions, and as accelerators or promoters in chemical reactions. The materials can also be used to impart properties to other chemical compounds such as mixing with liquids before polymerization to form metalized polymers or as pigments in coating materials such as in ceramics or paints.

The following examples are submitted in order to more particularly point out applicants invention and is not to be construed as a limitation upon the scope of the invention as set forth in the appended claims.

EXAMPLE 1 course of '16 hours. The precipitate was centrifuged and I reacted with 6 N KOH overnight to remove the initial Al(OH) andthat which had precipitated with the platinum. The remaining platinum was washed with water until it was neutral and was dried under reduced pressure for two hours. It Was mixed with one-half part of powdered polyacrylonitrile and one-half part of powdered polytetrafluoroethylene mounted in an -mesh metallic screen and pressed at a pressure of 200 psi.

The screen electrode was mounted in an electrochemical half cell for testing with liquid fuel on one side of the anode and 30% sulfuric acid electrolyte on the other at 100 C. Two runs were made. In the first run, decane was the fuel and methanol was the fuel in the second run. The electrode was operated anodically against a driven cathode, using a Luggin capillary and reference electrode to determine the polarization from theory at various current densities. The new catalyst was tested in comparison to two other commonly used platinum catalysts. The surface area of the catalyst was determined by the technique of triangular wave voltarnetry wherein the number of coulombs in the platinum oxide reduction peak being used as a measure of the number of platinum atoms in the surface. The results are set forth in the table.

1 In majcm. at 0.34 volt polarization for decane. 2 In Ina/cm. at 0.45 volt polarization for methanol. 8 As percent of theoretical monolayer.

As seen from the table, the catalysts prepared in accordance with the instant invention give at least 200% increase in activity over the best prior art catalyst.

EXAMPLE 2 An aqueous solution of a palladium chloride and excess mineral acid was added with stirring to an aqueous solution of NaAlO After the addition was complete, 37% formaldehyde-water solution, far in excess of that necessary to reduce the metal, Was added. The reaction mixture was allowed to stir overnight. The precipitated Al(OH) containing finely dispersed metallic palladium was separated by centrifugation and treated with 6 N KOH to dissolve off the Al(OH) The resulting large surface area palladium was then isolated by centrifugation.

EXAMPLE 3 Platinum-ruthenium was prepared in a manner similar to Example 2 using a mixture of chloroplatinic acid and ruthenium chloride. An aqueous solution of chloroplatinic acid and ruthenium chloride and excess mineral acid was added with stirring to an aqueous solution of NaAlO After the addition was complete, 37% formaldehydewater solution, far in excess of that necessary to reduce the metal, was added. The reaction mixture was allowed to stir overnight. The precipitated Al(OH) containing finely dispersed metallic platinum and ruthenium was separated by centrifugation and treated with 6' N KOH to dissolve off the Al(O I-I) The resulting large surface area platinum and ruthenium was then isolated by centrifugation.

EXAMPLE 4 An aqueous chloroplatinic acid solution is added to an aqueous solution of NaAlO Which has been treated with 30% aqueous H2804 to begin the precipitation of Al(OI-I) After the addition is complete, diborane is bubbled through the mixture overnight. The precipitated Al(OH) containing finely dispersed metallic platinum is separated and treated with 2 M H 80 to dissolve off the Al(OH) The resulting platinum has a surface area greater than that of platinum black.

What is claimed is:

1. A process of producing finely divided large surface area metallic precipitate which comprises:

(a) mixing in solution a soluble aluminum compound selected from the group consisting of soluble aluminum salt and soluble aluminum salt forming aluminum composition with a salt of a metal selected from the group consisting of Group IV-B, Group 4- V-B, Group VI-B, Group VIIB, Group VIII, Group LB, Group IIB, Group IIIB, Group IV-A and Group VA of the Periodic Chart of the elements;

(b) simultaneously reducing the metal salt from solution and precipitating the aluminum from solution in the form of Al(OII) by adding a metal salt reducing agent, said metal salt reducing agent selected from the group consisting of reducing agents which generate acid as the metal salt is reduced and reducing agents which generate base as the metal salt is reduced.

2. A process as claimed in claim 1 wherein the aluminum salt is selected from the group consisting of alkali metal aluminates, aluminum halides, and aluminum nitrate and the aluminum salt forming aluminum composition is aluminun metal with an alkali metal hydroxide.

3. A process of producing finely divided large surface area metallic precipitate which comprises:

(a) mixing in solution an aluminum compound selected from the group consisting of alkali metal aluminate and alkali metal aluminate forming composition with a salt of a metal selected from the group consisting of Group IV-B, Group V-B, Group VI-B, Group VII-B, Group VIII, Group I-B, Group IIB, Group IILB, Group IV-A and Group VA of the Periodic Chart of the elements;

(b) simultaneously reducing the metal salt from solution and precipitating the aluminum from solution in the form of Al(OI-I) by adding a metal salt reducing agent such that the reduced metal precipitates from solution, said reducing agent being a compound which generates an acid during the reaction step.

4. A process as claimed in claim 3 wherein said reducing agent is selected from the group consisting of formaldehyde, hydrazine, hydroxylamine, methanol, acetaldehyde, hydroquinone, isopropanol, formic acid and diborane.

5. A process as claimed in claim 3 wherein the solution of step (a) is titrated prior to the addition of the reducing agent with an acid until Al(OI-I) begins to precipitate.

6. A process as claimed in claim 3 wherein the precipitate from step ('b) is subsequently washed with a base.

7. A process of producing finely divided large surface area metallic precipitate which comprises:

(a) mixing in solution a soluble aluminum compound selected from the group consisting of soluble cationic aluminum salt and soluble'cationic aluminum salt forming aluminum composition with a salt of a metal selected from the group consisting of Group IV-B, Group VB, Group IIB, Group VI-B, Group VII- B, Group VIII, Group IB, Group II- B, Group III- B, Group IVA and Group VA of the Periodic Chart of the elements;

(b) simultaneously reducing the metal salt from solution and precipitating the aluminum from solution in the form of Al(OH) by adding a metal salt reducing agent such that the reduced metal precipitates from solution, said reducing agent being a compound which generates a base as the metal salt is reduced.

8. A process as claimed in claim 7 wherein said reducing agent is selected from the group consisting of sodium, sodium borohydride and methyl magnesium halide.

9. A process as claimed in claim 7 wherein the precipitate from step (b) is subsequently Washed with a base.

References Cited UNITED STATES PATENTS 7/1932 Pelc .5 7/1960 Hoekstra 75-108 

1. A PROCESS OF PRODUCING FINELY DIVIDED LARGE SURFACE AREA METALLIC PRECIPITATE WHICH COMPRISES: (A) MIXING IN SOLUTION A SULUBLE ALUMINUM COMPOUND SELECTED FROM THE GROUP CONSISTING OF SOLUBLE ALUMINUM SALT AND SOLUBLE ALUMINUM SALT FORMING ALUMINUM COMPOSITION WITH A SALT OF A METAL SELECTED FROM THE GROUP CONSISTING OF GROUP IV-B, GROUP V-B, GROUP VI-B, GROUP VII-B, GROUP VIII, GROUP I-B, GROUP II-B, GROUP III-B, GROUP IV-A AND GROUP V-A OF THE PERIODIC CHART OF THE ELEMENTS; (B) SIMULTANEOUSLY REDUCING THE METAL SALT FROM SOLUTION AND PRECIPITATING THE ALUMINUM FROM SOLUTION IN THE FORM OF AL(OH)3 BY ADDING A METAL SALT REDUCING AGENT, SAID METAL SALT REDUCING AGENT SELECTED FROM THE GROUP CONSISTING OF REDUCING AGENTS WHICH GENERATE ACID AS THE METAL SALT IS REDUCED AND REDUCING AGENTS WHICH GENERATE BASE AS THE METAL SALT IS REDUCED. 